Beneficiation of geological formations by means of underground nuclear detonations and the utilization of water in conjunction therewith

ABSTRACT

When a nuclear explosive device is detonated underground in a geological formation, an extraneous liquid such as water is introduced into the resulting fragmented area of the formation to upgrade the quality of fluid products withdrawn therefrom. For instance, water introduced into a chimney formed by underground nuclear detonation in a natural gas field may be used to remove water soluble radioactive contaminants from the gas to be produced from the formation. In another embodiment, the radioactivity of a water supply which is to be accumulated underground in a nuclearly detonated reservoir may be reduced to an acceptable level by introducing an initial volume of water into the fragmented formation about and above the point of detonation in an early stage of the accumulation process such that this water would scrub radioactive contaminants from the detonated formation and the contaminated water consequently accumulating in such early stage following detonation is removed before accumulation of substantially pure water is begun.

United States Patent 72] Inventor Rod P. Dixon Salt Lake City, Utah [21]Appl. No. 795,190 [22] Filed Jan. 30, 1969 [45] Patented Sept. 28, 1971[7 3] Assignee American Oil Shale Corporation Salt Lake City, UtahContinuation-impart of application Ser. No. 541,810, Apr. 11, 1966, nowabandoned and a continuation-in-part of 734,661, June 5, 1968.

[54] BENEFICIATION 0F GEOLOGICAL F ORMATIONS BY MEANS OF UNDERGROUNDNUCLEAR DETONATIONS AND THE UTILIZATION OF WATER IN CONJUNCTIONTHEREWITH [56] References Cited FOREIGN PATENTS 776,485 1/1968 Canada166/247 OTHER REFERENCES Carlsonz, Constructing Underground StorageFacilities with Nuclear Explosives," The Petroleum Engineer, August,i959, (pp. 834- 34).

Johnson et al.,: Nonmilitary Uses of Nuclear Explosives," ScientificAmerican, December [958, Vol. 199, No. 6, pp. 29.

Wainerdiz, Possible Use of a Nuclear Explosive For Stimulation of aNatural Gas Reservoir," Producers Monthly, August l965, vol. 29, No. 8(pp. 24- 25).

Primary Examiner-Stephen J. Novosad Attorney-Burns, Doane, Benedict,Swecker & Mathis ABSTRACT: When a nuclear explosive device is detonatedunderground in a geological formation, an extraneous liquid such aswater is introduced into the resulting fragmented area of the formationto upgrade the quality of fluid products withdrawn therefrom. Forinstance, water introduced into a chimney formed by underground nucleardetonation in a natural gas field may be used to remove water solubleradioactive contaminants from the gas to be produced from the formation.in another embodiment, the radioactivity of a water supply which is tobe accumulated underground in a nuclearly detonated reservoir may bereduced to an acceptable level by introducing an initial volume of waterinto the fragmented formation about and above the point of detonation inan early stage of the accumulation process such that this water wouldscrub radioactive contaminants from the detonated formation and thecontaminated water consequently accumulating in such early stagefollowing detonation is removed before accumulation of substantiallypure water is begun.

PATENIEU SEP28 I971 FIG] INVENTOR R00 P. DIXON ATTORNYS BY WCROSS-REFERENCE TO RELATED APPLICATIONS This application is acontinuation-in-part of copending applications Ser. No. 541,810, filedApr. ll, 1966, now abandoned and Ser. No. 734,661, filed June 5, 1968.

BACKGROUND OF THE INVENTION It is well known that a nuclear detonationunderground will create a cylinder or roofed-over chimney filled withbroken rock, normally with a void space at the top. This is broughtabout by a large, hot cavity filled with vaporized rock being createdabout the detonation point. The formation of the initial hot cavity asthe vaporized mass expands following the shock wave and the subsequentand progressive caving of the cavity roof and the formation of thecylinder of fragmented rock are very well known and do not requirefurther description. Such a cylinder of broken material contains chunksof fractured rock, which range randomly in size from sand grains to hugeboulders. Normally, there is a permeability between 25 percent and 40percent.

In such detonations radioactive elements are released in or as a resultof the detonation and thereafter may impart excessive radioactivity toproducts which are to be removed from the formation. For instance,tritium that is released in the detonation of a thermonuclear devicewill tend to contaminate natural gas that one may wish to recover fromsuch a formation. The contamination may be due to tritium in molecularform being mixed into the natural gas originally present in theformation, or at the very high temperatures which immediate ly follow athennonuclear detonation the tritium released may progressively becomepart of at least some of the hydrocarbon molecules present byinterchange with their original ordinary hydrogen atoms, or the tritiumreleased in the detonation may become converted to tritium oxide ortritiated water by combining with oxygen that may have been initiallypresent in the formation of the form of air or otherwise in molecularform or that may have been released by the detonation causingdisassociation of any of a number of mineral oxides commonly present inthe earth.

Other undesirably radiation products having a long half life, such asradioactive strontium, may also be formed in the formation of a resultof a nuclear detonation and cause contamination of products to berecovered from such a fracture formation.

If water is present or subsequently enters a nuclearly detonatedformation containing tritiated water or other water soluble radioactivedetonations products, the water itself then becomes excessivelyradioactive and unfit for inclusion in municipal water supplies or forother purposes where its radiation may constitute an impermissiblehealth hazard.

OBJECTS It is a broad object of this invention to provide a method forminimizing the hazards of radioactive contamination which attend thefragmentation of geological formations by underground nucleardetonations.

A more particular object is to minimize the contamination ofeconomically useful mineral fluids such as natural gas or water whichare to be recovered from a geological formation that has been fracturedwith the aid of a nuclear explosive device, and particularly athermonuclear device.

Another object is to reduce or eliminate the need for delaying productrecovery from a nuclearly detonated formation until after the radiationlevel drops to an acceptable value by natural decay, or to minimize theneed for removing radioactive contamination from fluid products aftertheir recovery from a nuclearly detonated formation.

A more specific object is to scrub radioactive matter such as tritium ortritium compounds from a nuclearly fractured formatron.

Another specific object is to create a nuclear cavity relatively freefrom radioactive contamination.

A still further specific object is to permit the recovery of fluidhydrocarbons from a nuclearly fractured formation after they have beenfreed from undesirable radioactivity or after their radioactivity hasbeen reduced to an acceptable level.

These and other objects, as well as the nature, scope, utility and modeof operation of the invention will become more clearly apparent from thesubsequent description and the attached drawings.

SUMMARY The present invention provides a process for reducing theradioactivity of a nuclearly fractured underground formation byintroducing above the point of nuclear detonation a volume of water orother liquid in which an unwanted radioactive contaminant is soluble,whereby the contaminant is scrubbed out and, if desired, can be pumpedout with the added liquid. More particularly, by placing a wash liquidsuch as water at an appropriate level in the formation prior to thenuclear detonation, the added liquid or the formation which isimpregnated with such liquid will absorb the radiation products when theformation collapses into the detonation cavity and carry the radiationproducts to the bottom of the fractured formation or chimney whence theresulting radioactive solution is pumped out or otherwise mechanicallyremoved for safe disposal while the desired useful fluid such as naturalgas is recovered separately from the contaminants.

When a nuclearly created cavity or chimney is to be used as anunderground reservoir for water or some other fluid such as natural gasthat is to be recovered later, the scrubbing of such a cavity or chimneywith water which is then pumped out in an early stage after a nucleardetonation while containing a relatively high concentration ofradioactive contaminants makes possible the subsequent accumulation andultimate recovery of relatively uncontaminated product fiuid from such areser- VOll.

IN THE DRAWINGS FIG. 1 is a vertical section through a mineral formationin which a nuclear entry hole has been drilled; a nuclear explosivedevice has been placed and freshly detonated; and water has been forcedinto the formation above and around the nuclear device and prior to thedetonation thereof for the purpose of absorbing and scrubbingradioactive contaminants from the gas phase following the detonation.

FIG. 2 is a vertical section through the same formation shown in FIG. 1but at a time substantially subsequent to the detonation. The nuclearlydetonated chimney is shown fully formed, with the water present in theformation prior to the detonation being collected at the bottom thereof,after intervening vaporization, condensation, and percolation downward,and ready for withdrawal through a recovery well.

GENERAL DESCRIPTION The production of minerals in situ from anunderground deposit has obvious advantages over the conventionalprocesses employing mining, breaking, surface treatment and furtherrefining when necessary. The use of nuclear explosive devices has arepresented major step forward in this connection, However, such use ofnuclear explosives, and especially the use of thermonuclear explosives,tends to release in the detonated formation radioactive substances whichmay cause the products withdrawn from such a formation to be injuriouslyradioactive and not suitable for use until such excessive radioactivityis reduced therein to a permissible level either by suitable treatmentor by radioactive decay which occurs when sufiicient time is allowed toelapse before the desired products are withdrawn from a nuclearlydetonated formation. As has been heretofore described by F. W. Stead,Science, Nov. 29, 1963, vol. 142, No. 3596, pages 1163 -l 165, theunderground explosion of a fusion device which is triggered by a smallfission device produces a considerably amount and variety of radioactivenuclides. However, most of these nuclides are relatively shortelived andtheir activities decrease rapidly such that at the end of one year theybecome insignificant in terms of recognized biological importance, andonly the longer-lived radionuclides remain to be seriously reckonedwith. Among these, the most important ones are H (tritium), Sr and Cs.C, while being relatively long-lived, is usually formed in only a verylow amount in an underground explosion because this nuclide is inducedby neutron reaction with N, and nitrogen is normally lacking in anunderground formation. Cs also usually should not be of majorsignificance because it tends to be relatively firmly held in the solidgeologic environment by exchange mechanisms. This leaves tritium, Srand, to some extent Co as the radionuclides that are most apt to be thecause of radioactive contamination in fluids removed from a nuclearlydetonated formation.

In a nonventing underground explosion, essentially all tritium wouldrapidly form tritiated water, either by oxidation or exchange, andtritium exchange between the tritiated water and the rock matrix shouldbe negligible. The resulting tritiated water would, of course, becomemixed with other underground water and impart radioactivity to it aswell as to any gaseous product which may be withdrawn from such aformation after becoming saturated or charged with vapor from theradioactive water present or formed in such a formation. Additionalcontamination of water in such a formation would result from thesolution of the radioactive strontium and cobalt in the water.

As an example, Stead, op. cit., has calculated the distribution oftritium and other radionuclides in ground water around a largeunderground fusion explosion, and more particularly around a l-megatonfusion explosion triggered by a lO-fission explosion. In making thesecalculations, it was assumed that the explosion is contained undergroundin the sense that the fireball and direct neutron flux does not reachthe atmosphere; the explosive device is surrounded by borated materialswhich capture neutrons without producing radioactivity; and theenvironment in which the explosion occurs consists of average crustalmaterials (such as dolomite or similar carbonate rock) with a porosityof 20 percent by volume and saturated with water.

The reaction products calculated for such an underground explosion areshown in table I.

TABLE I Reaction Products From Underground Explosion Fission InducedFusion products products pruducls Source (curies) (curies) (curies)Fission 10 KT) 3.0 X10" 10'' SR 1.5x l C5137 l x 0:l C" negligibleFusion (1 MT) H 6.7x 10" C 1O kilotons of fission release in a dolomiterock should produce the following effects: (i) a vaporized cavity radiusof about 1 10 meters, (ii) a crushed zone surrounding the cavity with anouter limit having a radius of about 230 meters, (iii) a grain densityof the dolomite of 2.8 and its porosity (water saturated) of 0.05 (5percent by volume). The radionuclides can be assumed to be distributedonly in the crushed zone by direct explosive action, and post-explosioncollapse of the crushed zone into the cavity does not effect the nuclidedistribution.

In such a system, the mass of solids in the crushed zone will be 1 14million metric tons, the mass of water in the pore space will be 2.1million metric tons, and the total mass will be about 1 16 millionmetric tons. c./g.

Assuming that Sr is all soluble and uniformly distributed throughout thedolomite in the crushed zone, its initial concentration in the totalmass of the crushed zone will be 1,500 curies Sr in l.l6 l0 g, or l.2910"'e./g.

When equilibrium is reached in the exchange of Sr between the dolomitematrix and the contained pore water, the amount of Sr in the water isexpressed by the equation Activity-solid Volume-water Activity-waterWeight-solid where K the distribution coeffi cient for dolomite, is 10.The Sr activity in the water is then 2.8 curies; and the Srconcentration in the water, 2.8 curies in 2.l 10 ml., is then l.3l3 l0"c./ml.

The minimum permissible concentration (on the basis of a l68-week for Srin water is l X10 c./ml., so that the initial Sr concentration in thecontained pore water in this example would be about the same as therecommended minimum permissible concentration. Of course, depending onthe concentration of clay minerals and other impurities in the dolomite,the Sr concentration in the water could be higher or lower than has beencalculated for the average" dolomite selected. Relatively impuredolomites would tend to lead to a lower Sr concentration, whereas puredolomites, with relatively large amounts of calcium and magnesium ionsin the pore water, would tend to lead to considerably higher Srconcentrations in water than shown in the above calculation.

Similarly the tritium concentration in the pore water in the above casewhich has been chosen as an example would be 6.7 l0 curies H in 2.14 l0ml., or 3.l 10 c./ml. The maximum permissible concentration (168-hourweek) for H" in water is 3X10 c./ml., so that the 11 concentration inthe water (about 1,700 acre-feet, or 2 10 mi) in the crushed zone in theselected example is two orders of magnitude higher than the recommendedmaximum permissible concentration and obviously would constitute ahighly undesirable health hazard.

ln accordance with the present invention, the previously mentioneddisadvantage of radioactivity is overcome by deliberately conductingextraneous water into the formation in an area above, and directlyabout, the point where the nuclear explosive device is to be detonated,although care is taken to keep the functioning mechanism of the deviceitself dry so as to assure its proper operation. The water is introducedin an amount sufficient to reduce the radioactivity in the watersolution after the nuclear explosion below a predetermined level. Theresulting dilution may be such that the diluted solution is directlysuitable for its intended use. Preferably, however the radioactive watersolution first formed after the explosion is pumped out for safedisposal elsewhere so as to permit the subsequent accumulation of onlylightly active fluid in the broken formation.

For instance, when a nuclear fusion device is to be used to increase thepermeability ofa natural gas field, an entry hole is drilled in thefield to the desired depth at which the device can be exploded withoutventing to the atmosphere. Thereafter, at a level somewhat above theanticipated location of the sintered layer of mineral which will resultfrom the nuclear detonation, and also about the nuclear device, thenecessary amount of water is injected; it may be pressurized in theformation as is otherwise done in conventional water fracturingoperations. As an alternative, extraneous water may be introduced intothe broken formation after the nuclear detonation through the nuclearentry well or other suitably located hole.

The invention will be further described in terms of particularillustrative examples.

EXAMPLE I In this example the invention is used to reduce theradioactivity of a natural gas field in which a thermonuclear explosionis used for stimulation or for increasing its permeability.

More particularly, referring to FIG. 1, the formation being ,treatedconsists of country rock which extends from the earth surface 1 to adepth indicated by 2, below which is the gasbearing stratum 4 whichextends to a depth of about 2,800 feet, with lean rock therebelow.

A 50 kiloton thennonuclear device 6 is placed in this fonnation throughnuclear entry well 5 at a depth of about 3,100 feet below the surface. Asupply of fracturing water 8 is injected into this formation at a levelabout 2,800 feet below the surface in an otherwise conventional mannerso that the water would extend laterally from the well preferably to adistance at least equal to the diameter of the cylinder to be created bythe subsequent detonation, e.g., radially to an extent of about 135 feetto 150 feet from the well. If desired, such water fracturing may beconducted at more than one depth to make certain that an adequate supplyof water is available in the formation to accomplish the desiredscrubbing and absorption of radioactive contaminants. Of course, afterone such detonation has been conducted in a given formation, the amountof water necessary for the scrubbing and absorbing operation in asubsequent shot can be predicted more accurately. It should beunderstood that when water is referred to in connection with such afracturing operation, various previously known thickening agents,propping agents such as sand and other desired additives may be includedtherein in accordance with conventional fracturing practice.

Instead of introducing the required water into the formation by a waterfracturing operation, when an adequate supply of water is availableeither at the surface or in the form of a subterranean aquifer, thiswater may be used for the underground scrubbing and absorbing operationby tapping it so that it would flow to the location in the formationwhere it is needed, or a combination of such tapping and waterfracturing can be used.

In conjunction with such water fracturing or other water insertion step,but usually subsequent thereto, a nuclear device 6 of the proper size isintroduced through the well 5, preferably after casing or otherwisesealing the latter so that the device may be inserted and maintainedsubstantially dry until the time of detonation.

As shown in FIG. 2, after the nuclear device is detonated in such anarrangement the supply of water 8 which has been inserted or otherwisesuitably channeled in the formation as shown in FIG. 1, drops down toform an aqueous layer 102 in the vicinity of the point of detonation asthe fractured formation settles down into the nuclearly created cavity 7(FIG. 1) and forms the type of cylinder or chimney of nuclearly brokenrock 101 as is otherwise well known in the art. To keep productcontamination at a minimum and also to reduce the risk ofunintentionally contaminating any subterranean aquifers that may bepresent in such a formation, it is preferably to sink a recovery well103 to the bottom of the fractured cylinder so that the contaminatedwater or other liquid accummulated therein as shown at 102 may be pumpedto the surface for appropriate safe disposal. Gas products relativelyfree from radioactive contaminants may be then withdrawn from an upperportion of the cylinder through a gas recovery well which may be thesame as the original nuclear entry well 5.

EXAMPLE 2 As a variation of the operation just described, this inventionmay be used to create an underground reservoir for water which may besubsequently included in a municipal water supply or for any otherpurposes without causing any undesirably radiation hazard. In such anembodiment, a nuclear explosive device 304 is detonated under nonventingconditions beneath an aquifer 303 which tranverses the formation, asschematically shown in FIG. 3. For maximum scrubbing effect, thedistance between the point of detonation of the nuclear device 304 andaquifer 303 hereabove should be such that the aquifer shall be above thehighest point through which the sintered layer, such as layer 9 in FIG.1, of the nuclear cavity passes after the nuclear detonation and priorto cave-in of the fragment formation thereabove. As a result, when thenuclearly detonated cylinder of fragmented rock (analogous to cylinder101 shown in FIG. 2) is formed under such conditions, the water from theaquifer 303 descends through the cylinder scrubbing radioactivecontaminants such as tritiated water as well as other water solublecontaminants and radioactive dust particles and collects at the bottomof the cylinder. After the detonation a recovery well, analogous to well103 shown in FIG. 2, is then drilled to extend to the bottom part of thecylinder and the contaminated water accumulating therein is then pumpedout and its radioactivity checked by a Geiger counter or otherappropriate, well-known means. When the radioactivity in the withdrawnwater has dropped to an acceptable level, the pumping may be stopped andpure water allowed to accumulate in the cylinder for subsequentwithdrawal as and when needed. It is particularly desirable to pump thecontaminated water from the cylinder at a rate grater than the downwardflow of water in the cylinder, so that the contaminated water may besubstantially completely deplete from the cylinder and accumulation ofpure water therein may be begun at a relatively early time after detonation.

The scope of the invention is more particularly pointed out in theappended claims.

1. In a process for fragmenting and beneficiating a geological formationby an underground nuclear explosion which is set off under nonventingconditions and whereby a roof topped, underground chimney of fragmentedrock is formed with a gas phase in the void spaces in the chimney andwhereby radioactive contaminants are released in the forma' tion, theimprovement which comprises introducing extraneous liquid into theformation above the detonation point such that the liquid after theexplosion and consequent chimney formation descends downwardly throughthe fragmented formation, scrubs radioactive contaminants therefrom andcollects at a lower portion of said chimney, and decontaminating saidfragmented formation for further use by mechanically removing saidcontaminant-containing liquid therefrom separate from decontaminatedmineral product.

2. A process according to claim 1 wherein the extraneous liquid iswater, the explosion is a fission explosion and the resultingcontaminants comprise radioactive strontium in water-soluble form.

3. A process according to claim 1 wherein the extraneous liquid iswater, the explosion is a fusion explosion and the resultingcontaminants comprise tritiated water.

4. A process according to claim 3 wherein the extraneous water isintroduced into the formation prior to said explosion at a locationwhich is above the point of detonation and within that portion of theformation which becomes fragmented by said explosion.

5. A process according to claim 3 wherein the extraneous water isconducted to an upper portion of said chimney of fragmented rocksubsequent to the explosion.

6. In a process wherein an underground reservoir for water having anacceptable radioactivity level is created by a subterranean nucleardetonation in a geological formation which is traversed by asubterranean aquifer and wherein radioactive contaminants are releasedby said detonation,

the improvement which comprises placing a nuclear explosive in saidfonnation at a depth sufficient to avoid venting to the atmosphere andsuch that upon detonation of the explosive and creation of a nuclearcavity prior to formation cave-in said aquifer is located above saidcavity,

detonating said explosive and thereby causing fragmentation of theformation thereabove and formation of a cylinder of permeable brokenrock with a gas phase between the broken rock extending from the pointof detonation up into said aquifer, whereby water from the aquiferdescends through said cylinder scrubbing the said gas phase andaccumulating in a lower portion thereof,

drilling a recovery well from the surface to where said water andradioactive contaminants contained therein accumulate,

pumping said accumulated contaminated water from said cylinder until theradiation level of the removed water drops below a predeterminedacceptable value,

and thereafter accumulating acceptably pure water in said cylinder forlater recovery.

7. A process according to claim 6 wherein contaminated water is pumpedfrom the cylinder at a greater rate than water from the aquifer descendsthrough the cylinder, whereby the contaminated water is substantiallydepleted from the cylinder before acceptable pure water is permitted toaccumulate therein.

8. In a process for fragmenting a natural gas bearing geologicalformation by an underground nuclear explosion which is set off undernonventing conditions and produces a rooftopped underground chimney ofrock fragments with a gas phase in the void spaces therebetween andreleases radioactive contaminants in the formation,

the improvement which comprises:

introducing liquid into the fonnation above the explosion point suchthat the liquid after the explosion and consequent chimney formationdescends downwardly through the formation, scrubs radioactivecontaminants therefrom and accumulates at a lower portion of saidchimney,

and removing natural gas relatively free from radio-active contaminantfrom an upper portion of the formation after the formation has beenfragmented and the gas therein has been scrubbed with said descendingliquid.

9. A process according to claim 8 wherein the extraneous scrubbingliquid is water.

10. A process according to claim 8 wherein the contaminants containtritium, the extraneous scrubbing liquid is water, and the accumulatedcontaminant-containing water is removed from the formation for safedisposal at the surface separate from the natural gas product.

2. A process according to claim 1 wherein the extraneous liquid iswater, the explosion is a fission explosion and the resultingcontaminants comprise radioactive strontium in water-soluble form.
 3. Aprocess according to claim 1 wherein the extraneous liquid is water, theexplosion is a fusion explosion and the resulting contaminants comprisetritiated water.
 4. A process according to claim 3 wherein theextraneous water is introduced into the formation prior to saidexplosion at a location which is above the point of detonation andwithin that portion of the formation which becomes fragmented by saidexplosion.
 5. A process according to claim 3 wherein the extraneouswater is conducted to an upper portion of said chimney of fragmentedrock subsequent to the explosion.
 6. In a process wherein an undergroundreservoir for water having an acceptable radioactivity level is createdby a subterranean nuclear detonation in a geological formation which istraversed by a subterranean aquifer and wherein radioactive contaminantsare released by said detonation, the improvement which comprises placinga nuclear explosive in said formation at a depth sufficient to avoidventing to the atmosphere and such that upon detonation of the explosiveand creation of a nuclear cavity prior to formation cave-in said aquiferis located above said cavity, detonating said explosive and therebycausing fragmentation of the formation thereabove and formation of acylinder of permeable broken rock with a gas phase between the brokenrock extending from the point of detonation up into said aquifer,whereby water from the aquifer descends through said cylinder scrubbingthe said gas phase and accumulating in a lower portion thereof, drillinga recovery well from the surface to where said water and radioactivecontaminants contained therein accumulate, pumping said accumulatedcontaminated water from said cylinder until the radiation level of theremoved water drops below a predetermined acceptable value, andthereafter accumulating acceptably pure water in said cylinder for laterrecovery.
 7. A process according to claim 6 wherein contaminated wateris pumped from the cylinder at a greater rate than water from theaquifer descends through the cylinder, whereby the contaminated water issubstantially depleted from the cylinder before acceptable pure water ispermitted to accumulate therein.
 8. In a process for fragmenting anatural gas bearing geological formation by an underground nuclearexplosioN which is set off under nonventing conditions and produces aroof-topped underground chimney of rock fragments with a gas phase inthe void spaces therebetween and releases radioactive contaminants inthe formation, the improvement which comprises: introducing extraneousliquid into the formation above the explosion point such that the liquidafter the explosion and consequent chimney formation descends downwardlythrough the formation, scrubs radioactive contaminants therefrom andaccumulates at a lower portion of said chimney, and removing natural gasrelatively free from radio-active contaminant from an upper portion ofthe formation after the formation has been fragmented and the gastherein has been scrubbed with said descending liquid.
 9. A processaccording to claim 8 wherein the extraneous scrubbing liquid is water.10. A process according to claim 8 wherein the contaminants containtritium, the extraneous scrubbing liquid is water, and the accumulatedcontaminant-containing water is removed from the formation for safedisposal at the surface separate from the natural gas product.